Project cannot save - file cannot be opened

[Guloluseus]

Morning all

Have a feeling I am not the only one coming across this. Every so often I will try to save (or save as) my current project, ad get an error


"The file "xxxxx.mpp" cannot be opened.
Check that the file name and path are correct.
..."

It is very frustrating to spend time marking up, changing, etc a prog only to find that with no warning MSP decides its had enough!

To summarise- trying to save n MSP 2013 file as a 2013 file or an MSP07 file, cannot save for the above error. I can work on it, print it, but not save or save as... . There is no warning message prior to this.

EDIT: found a possible resolution in that SP1 is supposed to resolve this, however checking version number shows that SP1 is already installed.
Just lost my first 30 mins work so today can only get better